ABSTRACT
The study of magnetohydrodynamics is the study of how a fluid which consists of charged point particles moves in the presence of electromagnetic fields. The study is done in the fluid approximation in which the properties of the particles are averaged over volumes which are small compared with macroscopic volumes but large compared with the interparticle distance. In the simplest picture of a plasma, we can consider two interpenetrating fluids, one consisting of electrons and one of positive ions. Each fluid moves with its own velocity. These velocities are approximately equal but their difference gives rise to the currents. A cold plasma can be regarded as one in which each particle moves with the mean fluid velocity so that there is no thermal motion. The force exerted on each particle is given by the Lorentz force law. In warm plasma, the particles have a thermal distribution of velocities and the plasma exerts a pressure.
